This invention relates generally to keyboards and more particularly to low profile keyboards having tactile feedback of switch actuation.
Keyboards which have a low profile, that is keyboards that are thin, are well known in the art. Such keyboards are particularly useful where it is desired to use as little space as possible, as in television tuners, hand held calculators and the like. One of the characteristics inherent in low profile keyboards of course is that the distance the key travels to effect actuation of the switch controlled by the key is short compared to the type of key switch known in the art as desk top or travel type key switches such as those frequently used in computer terminals, typewriters and the like where more space is available and in applications where the operator is accustomed to experience more key travel for key switch actuation to provide assurance that a switch has in fact been actuated upon depression of the respective key.
In low profile keyboards it is also highly desirable to provide assurance to the operator that the switches are actuated when the keys are depressed. One way that this is accomplished in prior art keyboards is by employing snap acting members in conjunction with the keys. That is, the key is arranged so that upon depression by a user, force is applied to a snap acting member such as a dished shaped disc which snaps from a convex configuration through a plane formed by the periphery of the disc to a concave configuration thereby causing actuation of a switch. The sudden movement of the disc as it snaps from the one configuration to the other is tactily felt by the operator through the key. Examples of this type of keyboard may be found in U.S. Pat. Nos. 3,959,611; 3,952,174 and 3,893,235 which illustrate but a few of such keyboards.
The advent of digital keyboard controls for appliances such as microwave ovens has resulted in the requirement of a keyboard which is easily cleanable and devoid of crevices which would tend to collect food particles and the like. Frequency responsive and capacitive type keyboard controls can be constructed having these characteristics by employing a flat smooth outer face having indicia thereon to identify the key locations. This type of keyboard is highly conducive to cleaning however it offers no tactile feedback and generally is more expensive than an electromechanical keyboard.
Keyboards of the type set forth in the above patents, as previously stated, provide excellent tactile feedback even with a thin layer of flexible electrically insulative material such as polyethylene teraphthalate to seal the switches and maintain the disc elements in their proper location; however, if a flat relatively stiff membrane is disposed over these keyboards, for instance to facilitate cleaning by providing a flat smooth outer face, the tactile feedback is deleteriously affected. The membrane requires a certain amount of inherent stiffness in order to maintain its flatness however this stiffness effectively masks the tactile feedback.
It is therefore an object of this invention to provide a low profile keyboard which is easily and readily cleanable as well as one which provides tactile feedback of switch operation. Another object is the provision of a keyboard which is inexpensive yet reliable having a flat, smooth top surface with tactile feedback of switch operation. Yet another object is the provision of a tactile feedback keyboard having snap acting discs with a flat cover overlying the discs with indicia marked thereon to identify the location of keys. Another object is the provision of means to ameliorate switch actuation when an operator depresses the top surface at a location somewhat off center of a key switch. Other objects and features will be in part apparent and in part pointed out hereinafter.
Briefly, in accordance with this invention keyboard apparatus having a flat top surface overlies a substrate mounting a plurality of spaced stationary contacts and intermediately disposed electrically conductive, snap acting disc elements which upon depression are snappable from a first convex configuration to a second concave configuration and are so arranged that snapping of a disc switches or closes a circuit path. Tactile feedback of switch actuation is obtained by interposing a tactile feedback member between the discs and the flat top surface. Several different tactile feedback members are shown including rigid plate like members captured in a frame circumscribing each disc or secured to a sheet so that a plate member is held at each switching station. The sheet can be the flat cover itself with the individual plate like members adhered to the bottom surface thereof or it can be a separate carrier sheet provided with apertures which receive depending posts from the tactile feedback members subsequently headed over in rivet like fashion to securely attach the members to the carrier sheet. In another embodiment the member comprises a single sheet of material extending over two or more switching stations with protrusions formed in the sheet aligned generally with the center of the discs. Ribs may be formed in the sheet extending from each protrusion to add rigidity to the localized area adjacent the protrusions thereby permitting the switching stations to be spaced further apart. Motion decoupling means may be employed to prevent motion from one switching station from affecting adjacent switching stations. The decoupling means is shown as a series of slots in the tactile feedback sheet extending generally along and adjacent a portion of the boundaries of each switching station or a plurality of projecting supports depending from the tactile feedback sheet, the supports located adjacent the boundaries of the switching stations and extending from the sheet in the same direction as the protrusions.